It is well known that complex electromechanical devices, such as computer disc drives, can be harmed by foreign substances which come into contact with vital components of the device. For example, dirt or dust particles which accumulate on the platters of a disc drive can damage the read/write head of the drive causing a "crash." Thus, such devices are typically manufactured within a clean room environment and are sealed prior to leaving the clean room to reduce or prevent the possibility of such contamination.
However, the current breed of disc drives spin much faster and are more densely packed with data than prior drives. These speed and size increases require that the read/write heads fly very close to the surface of the disc platters (on the order of a micron). In light of these very low fly heights, it is possible for matter smaller than common dust or smoke particles to cause head/disc crashes. Indeed, even chemicals or chemical compounds which are outgassed by the different components of the disc drive may be sufficiently large to interfere with the drive heads.
Although some disc drive components outgas chemicals and chemical compounds while the drive is inactive, the level of outgassing typically increases when the drive is operating and the components are exposed to high temperatures. These outgassed chemicals and chemical compounds are easily transported throughout the drive (due to the rotation of the disc platters and the resulting air currents within the drive) where they typically bond to the substrate that coats the disc platters. In addition to physically interfering with the drive heads during operation of the drive, some aggressive outgassed compounds (e.g., adhesives) may react chemically with the drive heads during periods of inactivity when the heads are in direct contact with the disc platters. Such chemical reactions cause stiction between the heads and the disc platters which further contributes to early disc drive failure.
Thus, it is important for disc drive manufacturers to carefully inspect all of the components which make up the drive for the presence of outgassed compounds. Examples of such components within a disc drive include voice coil motors, coil bobbins, magnets, read/write heads, adhesives and labels. One specific disc drive component that may contribute greatly to the total outgassing of a disc drive is the spindle motor.
FIG. 1 illustrates a typical prior art spindle motor 20. The motor 20 includes a base 22 which is fixed to a base plate 24 (FIG. 2) of a disc drive 26. A hub 28 (FIG. 1) of the spindle motor 20 rotates on a bearing (not shown) about a shaft 30 connected to the base 22. In this manner, the hub 28 is free to rotate in relation to the base 22 of the spindle motor 20. The base 22 typically includes electrical windings (not shown) while the hub 28 typically includes magnets (not shown) which interact with the magnetic field created when an electrical current passes through the windings (not shown) within the base 22. Thus, the base 22 acts as a stator while the hub 28 acts as a rotor of the spindle motor 20.
One or more disc platters 32 (FIG. 2) are attached to rotate with the hub 28 about the fixed shaft 30. A separate voice coil motor 34 operates to move one or more arms 36 over the spinning disc platters 32 so that magnetic read/write heads 38 can access any part of the disc platters 32. In current disc drives, the spindle motor 20 may be required to spin at speeds up to 10,000 revolutions per minute (RPM). This high speed operation, together with the large number of components which make up a spindle motor (e.g., magnets, wiring, bearings, adhesive seals, etc.), causes the spindle motor 20 to outgas a variety of compounds. Although the spindle motor 20 outgasses compounds even when the motor 20 is idle, the outgassing levels increase dramatically during operation of the spindle motor. Specifically, many of the components within the spindle motor 20 may outgas compounds which are normally retained within the motor 20 while the motor is at rest. However, when the motor 20 spins up to an operating speed of 5,000 to 10,000 RPM, centrifugal force tends to expel these compounds from the interior of the motor 20 to the interior of the drive 26.
Unfortunately, prior outgassing test systems typically test the spindle motor in an idle or non-operative state. Specifically, one type of outgassing test, hereafter referred to as "static headspace sampling," entails placing a component (such as the idle spindle motor 20 shown in FIG. 1) within a sealed container and holding the component at an elevated temperature until the outgassed compounds reach a state of equilibrium within the headspace. The term "headspace" is utilized herein to refer to the space within the sealed container which is not taken up by the tested component itself. The sealed container typically includes an open top sealed by a septum to allow a needle to penetrate the headspace and withdraw a sample of the equilibrated headspace. This sample is then analyzed using known techniques and equipment such as a gas chromatograph and a mass spectrometer to determine the composition of the different outgassed compounds. However, while testing the spindle motor 20 at an elevated temperature may simulate the heat which is generated by an operating spindle motor 20, any additional compounds outgassed at the elevated temperatures will likely remain confined within the interior of the non-operative motor itself.
One alternative to the static headspace sampling test entails placing the component to be tested within a test container and then passing an inert gas through the container during the course of the test to continuously flush outgassed compounds from the container. This is referred to as a dynamic headspace outgassing test. However, the dynamic gas flow applied to the test container during the dynamic headspace outgassing test is not typically strong enough to expel outgassed compounds from the confines of the idle spindle motor 20. Thus, regardless of whether a static or a dynamic outgassing procedure is used to test the spindle motor 20, neither test provides a sufficiently accurate or representative indication of the types and amounts of outgassed compounds which an operative (i.e., spinning) spindle motor 20 produces and expels within the interior of a functioning disc drive 26.
A further concern with prior art spindle motor outgassing tests is that the entire spindle motor 20 (FIG. 1) is typically placed within the testing container (regardless of whether the container is used in a static or a dynamic testing system). However, FIGS. 2 and 3 illustrate that only a portion of the spindle motor 20 is exposed to the interior of the disc drive 26 so that testing the entire spindle motor 20 may lead to the detection of outgassed compounds which would not normally be found within the interior of the drive 26 (i.e., a false positive reading).
FIG. 2 illustrates an exploded view of a disc drive 26 showing the base plate 24 of the drive together with a top cover 40 and a printed circuit board assembly (PCBA) 42 which are attached to opposite sides of the base plate 24. The top cover 40 fits over the voice coil motor 34, the arms 36, the disc platter(s) 32 and the spindle motor 20 to form a substantially sealed interior volume of the disc drive 26. The disc platters 32 are cut away in FIG. 2 to better illustrate the spindle motor 20 mounted to the disc drive base plate 24. The base plate 24 includes an opening (not shown) for receiving the base 22 of the spindle motor while an outwardly protruding annular flange 46 of the base 22 (best shown in FIG. 1) is preferably attached to a top surface 48 of the disc drive base plate 24 by a plurality of screws 50. Attached in this manner, the base 22 of the spindle motor 20 extends below the base plate 24 of the disc drive, as shown in FIG. 3, and thus is not exposed to the interior volume of the disc drive 26.
One significant element of the spindle motor 20 which extends below the base plate 24 of the disc drive 26 is the electrical connector 52 (FIG. 1) which provides power for operating the spindle motor 20. Specifically, the electrical connector 52 is attached to a lower portion of the spindle motor base 22 so that a number of electrical leads 54 extend radially outwardly from the base 22 below the annular flange 46. The electrical leads 54 are positioned to contact matching electrical pads 56 (FIG. 2) on a top surface 58 of the PCBA 42 as the base 22 of the spindle motor 20 extends through a circular opening 60 formed in the PCBA 42. The electrical pads 56 supply power to the connector 52 for operating the spindle motor 20 once the PCBA 42 is connected to a power supply/motor controller (not shown). Furthermore, the connector 52 is typically attached to the spindle motor base 22 by an adhesive material, and the presence of the connector 52 and the adhesive material within the prior art testing container frequently contributes false positive readings to prior art outgassing tests.
Thus, prior art outgassing tests of disc drive spindle motors produce inaccurate or unrepresentative results for two primary reasons. First, the motors are typically tested in an idle state where the hub or "rotor" 28 is not rotating so that outgassed compounds within the motor 20 are not expelled into the headspace of the testing container. Second, the motors are typically tested as a whole so that the outgassing results include contributions from components of the motor 26 which are not typically exposed to the interior volume of the disc drive 26.
It is with respect to these and other background considerations, limitations and problems that the present invention has evolved.